Prevention of knock in internal combustion engines



Dec. 15,

1942. J, M. CAMPBELL PREVENTION OF KNOCK IN Y1\Y'IEl' l\IAL GOMBUSTION ENGXNES Filed Aug. 24, 195e 3.o camo/54 @fw/VOLS) TUR/4.5mm 40 Pff GALLO/v Patented Dec. 15, 1.942

PREVENTION OF KNOCK 1N INTERNAL COMBUSTION ENGINES John M. Campbell, Detroit, Mich., assigner to General Motors Corporation, n corporatlonof Delaware Detroit, Mich., a

Appuunn'august 24, 1936, serial No. 97,525 U 1o claims. (c1. 4i-9l' The invention relates to fuelmixtures and their l use in internal combustion engines, more particularly engines of the #high-compression type, i. e., those in which the usual commercial pe-v troleum hydrocarbon fuels, without admixture of special antiknock agents, will produce fuel knock.

'I'he object of the invention iis to overcomesome disadvantages that have been found in y'the use kof tetraethyl lead'as an antiknock agent and in general to improve the operation of multicylinder engines using low-compression fuels, i. e'., fuels that require additions of antiknock agents.k

It hasy been found that the effectiveness of antiknock agents of thelead alkyl type variesc considerably notonly with the molecular constitution of the compounds-but also with conditions of fuel, of fuel-air mixture, and ofengine operation.

I have ascertained, by roadl tests on standard multicylinder automobile engines, including popular cars of the six-cylinder and eight-cylinderv types, that at relatively lowV speeds and/or low temperatures certain gasolines containing lead alkyls show peculiar eccentricities in their knocking characteristics with different antiknock compounds as lcompared with their behavior ln single cylinder engines. The tests show, for example, using a straight run gasoline,l that with a commonly used addition'of lead .tetraethyl (3 c. c. per gallon) the fuel would rate as much as six octane numbers below what it should show by the usual A. S. T. M. rating, based upon the oper-l n ation in a single cylinder engine. Similar apparent depreciation, but to an even greater extent, was found `with addition of lead tetrapropyl.

cated that increase in mixture temperature tended to lessen the apparent deviations from results that wouldy be expected f rom determinations made with single cylinder engines.

In the accompanying drawing? is shown in graphic form the relative effectiveness at varying v engine speeds of equal quantities of lead-supplied` respectively in 3 c. c. per gallon of tetraethyl lead, 2.53 c. c. dimethyl diethyllead, 2.06 c. c. tetramethyl lead, and equimolecular amounts of tetramethyl' and tetraethyl lead mixed. These data show results of road tests on a straight eight cylinder automobile.

In the ltabular presentation of these data the car speed is represented by abscissas and the knock intensityl by` ordinates. The dotted lines A, B, C, represent the knocking effectin the engine 4of three reference fuels containing no added antiknockagent and whose octane ,ratings were respectively 65, 70, and '75. These three fuels were tested'v merely to determine .reference lines for comparison with the several additions to the fuel under investigation. It will be noted y that the knock curves of the reference fuels drop oi! gradually as the speed increases so that the knock substantially disappears with the 65 octane fuel at about 37 M. P. H., with the 'l0 octane fuel at about 29 M'. P. H. andwith the 75 octane fuel Additions of lead tetramethyl, on the other hand,

resulted in an improvement in antiknock effect to the extent of four or five octane numbers above the A. S. T. M. rating. These variations were' especially marked during acceleration from low speeds. I

I found also that with relatively volatile fuels, particularly gasolines containing a considerable proportion ofthighly volatile hydrocarbons, as pentane and hexane, these differences vwere accentuated, the higher alkyls being even less eective and the lower alkyls more effective than in less volatile fuels. lurthei` trials showed variations in the eiiectiveness oi' different lead alkyls .with changesin the engine speed, viz., thatthe higher alkyls, as lead tetraethyl and lead dimethyl diethyl, improved in eiectiveness with increase in speed, whereas lead tetramethyl became less effective, for the same lead content,

as the engine speed increased. Other tests'indi 55 at about 19 M. P. H. l

The fuel under investigation, a gasoline containing considerable amounts of highly volatiler hydrocarbons and having a relatively wide range l of volatility, was tested with four different antiknock agents as specied. The curve D (dot and dash line) represents the effect of tetraethyl lead, the curve E, (light full line) the effect of tetra-f methyl lead, the curve F, (heavy lfull line) the effect of the mixture of. tetramethyl and tetraethyl ylead and the curve Gy (broken line) the effect of dimethyl diethyl lead.

As indicated by these curves, the tetraethyl lead is the least effective of the ,four antiknock agents at engine speeds up to about twentyrniles A per hour of car speed (about 1,000 R. P. M. of engine speed), tetramethyl lead isk much more effective at speeds up to twenty miles per hour but increasinglyless effective at higher speeds,

and the mixture of thek tetramethyl and tetraethyl lead averages to a large extent the effect of th'e two constituents. Dimethyl diethyl: lead,

however, is not subject to the defects of either4 of the other alkyls but parallelsvery closely the normal octane curves of the untreated reference fuels. ,7.

Since lthe antiknock'eifect of tetraethyl `lead is l`and to a considerable extent at 2 higherthan that of tetramethyl lead, based upon the same'lead content, when determined in a th'e unexpected sensitiveness toV knock inthe standard multicylinder engines of fuels treated with tetraethyl lead and theimprovement noted at low speeds and during acceleration from such single cylinder engine, it was my conclusion that speeds with the use of a normally (in asingle cyl index' engine) lessheife'ctive lower ,alkyl such vas tetramethyl lead, or with the use of mixed alkyls,

were due, at least in part, to lack of uniformity in the distribution of the fuel constituents and antilrnoclr agents. This conclusion is reinforced further by the fact, which I have also observed, that the departures noted in multicylinder engines from the estimated effect based upon single cylinder tests largely disappear at higher .speeds higher mixture or engine temperatures.

It is wen known that the distribution of gasoline to the cylinders of av multicylinder engine varies considerably both as to quantity and qual-I `ity, particularly at lower speedsand temperatures At high engine speeds the liquid gasoline carried intothe intake systemis more uniformly distributed to the cylinders due to the increasedturbulence andthe higher" carrying capacity of the swiftly moving air stream. jI-Iigher temperatures of mixture or engine. parts with which the fuel contacts such as hot spots, or

of the air constituent of the fuel also reduce the proportion of fuel that remains in liquid form.`

However, the present trend of engine ldesign is generally to reduce the application of heat to the fuel. This trend naturally results fromfthe generalvavailability of engine fuels of greater volatility and the eifortto increase volumetric emciency by reducing mixture temperatures. q l.

'As to the quality of the fuel charges delivered toV the various cylinders," the `more volatile fuel constituentswill. of course, be more readily va`V porized. Hence--the charges willvarywin proportions of unequally volatile constituents of the fuel when the portion remaining" liquid is not" uniformly distributed. 'l'h'at is, some cylinders, receiving less of the liquid portions of the fuel, will receive a higher proportion of the more volf atile fractions while the cylinders `into which moreof the liquid portions of thefuelis carried will receive a larger proportion of thevl'ess volafractions of higher antiknock yalue,n1ay actually have the greater tendency. to'` knockwhen the fuel iis only partially-vaporized inthe intake system. d

This refers particularly, of course, to the desirable ranges of power output since it is known that mixtures maybe made so lean as to reduce knock intensity by mere leanness but withserious -loss oflpower, f' n During rapidacceleration thesudden introf duction of additional fuel vandthe rush of air `over liquid-laden parts'of'the intake system still further complicate the situation since it is practically impossible to distribute liquid fractions Athe leaner cylinders, although receiving fuel` 'rst figure representing lthevapor pressure-atuniformly to multiple cylindersY once thev` liquid is deposited upon the walls ofthe intake passages.,-

When the throttleis suddenly opened thehlgher f lead'alkyls also seemtolag :behind the lighter fuo1 constituents nndoimg 'tothe waus ortho intake passages Since, as Ihave observed, their antiknock effect gradually increases after alcceleration when the speed is5kept constant fora time and thev lead alkyls,.;which are at first deposited on the manifold walls, arehflnally *swepty int'o the. cylinders. 4 K y 1 l Y It will be appreciatedthatf from 'the stand- 'point ofthe driver, knocking; in any cylinderis disagreeable,`-and is also detrimental fromfthe,

, viewpoint of operative ,eiliciency.v -In accordance` g with the present'invention, therefore, itis proposedV to correct `or reduce the erratic knocking tendency in multi-cylinder engines by use' of vantiknock agent ofthe lead alkyl` type falling*` 'between lead tetramethyl and`lead tetraethyl whose effectiveness under certain ycondititins superior to that of either. Such conditionsocr j i y i ordinarily at low speeds and temperaturesand` `particularly during acceleration'from low The exact limits within which the superiority-,ofc the ymixed alkyls is mostmarked will .varyyof course, with enginev type and design. butmay-be'fi o generally found t in s multicylinder` Y engines.' at engine speeds of o-to 1500 R.P.'M. under'open throttle operation or during accelerationfjjl'hejf: -duration of the periodfof imperfectv distribution and deposition-of the antiknockmaterialon'the.1 l

walls of the induction system,"and resultant accentuated tendency Vto lnrlocky in some 'cylinders naturally may vary withfthe seasonal conditie/nsfv L v in any given engine. In my experiments theore;v t duced eillciency of tetraethyl lead has-'been *f particularly at mixture temperatures below about,4

' The advantage, from the viewpoint of volovtility, of the use of mixtures of `lead alkyls or"of-` d the nlixedialkyls per se will be appreciated from` a comparison of the vapor pressures of there-1 A spective alkyls. According Vto the latest-"detr"Ar` minations for which data are available lthe vapor pressures of the respective alkyls, expressed "in':

millimeters of mercury, range asfollows: the

Phanave-2.55715 n PbMoEts-; PbMezEtz PbMetEt k. '1543sy i PbMel 45o-10er The two temperatures mentionedoare significant? since they represent approximately the c f temperature range typical of apresent automobile engine in normal-operation: Stilllowerv temperatures-of course, mayprevail during :thee` Warmingfup period andin'cold weather. -L j With respect to inherent antiknock edect'o' the lend slkyistotrnmethyiiead is distinctly 1era-` efllcient, forV the same-lead .content thanftetrai` ethyl lood, trimothyl otny1 load lsjobout naif woylkv I between tetramethyl andxtetr'aethyl leadprar'idVV the other two methyl-ethyl compounds are'ofapproximatelyfthe same value yas `tet'raethyl lead;` l i These values arebased upon complete vapori'zationl conditions which probably seldom exist inf' present engines with ordinary commercial""g'aso-,J` lines and my experience indicates that, under they i conditions under which knocking most frequentl'y occurs in normal o peration,'the mixed alkyls arer I distinctly superior` to tet-raethyl lead;r

Considering only the volatility factor, the use of an antiknock agent comprising a. mixture of lead alkyls having tetramethyl lead as a constituent would be advantageous since it would enable theleaner cylinders which tend to knock to receive a mixture rich in antiknock agent.

I have found, however, that the desirable properties of the lower and higher alkyls are better combined when both the methyl and ethyl radicals are present in the molecular structure. For example, as shown on the drawing, dimethyl diethyl lead was superior, inthe engine tested, to a mixture of tetramethyl and tetraethyl lead at all speeds observed.

While I prefer the dimethyl diethyl lead as best combining the desirable effects of the higher and lower alkyls in the methyl-ethyl lead group, it will be understood that the other members of the group also realizeto some degree the respective advantages of the combined radicals. A

Reference is made to U. S. Patents 1,592,954 and 1,668,022 for disclosures of the manner of utilizing the lead alkyls in commercial practice.

I claim:

1. A fuel for high-compression multicylinder internal combustion engines comprising a. mixture of hydrocarbons of such varying volatility as to cause material variation in the knocking` tendency in different cylinders andra relatively small amount of dimethyl diethyl lead.

2. A fuel for high-compression multicylinder internal combustion engines comprising a mixture .of hydrocarbons of such varying volatility as to cause material variation in the knocking tendency in different cylinders and a small quantity of dimethyl diethyl lead sufficient to substantially correct the variation in knocking tend-` ency.

3. Method of preventing fuel knock in a multicylinder internal combustion engine comprising supplying thereto a gasoline whose volatility is such as to result in some cylinders receiving an air-fuel mixture tending to knock and other cylinders an airfuel mixture having `less 'tendency to knock and supplying with such gasoline a relatively small quantity of dimethyl diethyl lead sufficient to substantially correct thedifl'erenc in tendencies to knock.

4. The process of operating a multicylinder internal combustion engine duringacceleration from low speeds comprising supplying to said engine ya mixture of air and fuel, the conditions being such that a material portion of the fuel is in liquid form in the intake passages of the engine and is unequally distributed to the cylinders, and supplying with the fuel mixture a relatively small amount of dimethyl diethyl lead.

5. Liquid fuel for internal combustion enginesv of the Otto cycle multicylinder type comprising a mixture of khydrocarbons of such varying volatility and forming such varying air-fuel ratios as to cause material variation in the knocking tendency of the several cylinders in operation and containing a small quantity of a mixture comprising tetraethyl lead and amore volatile lead alkyl than tetra ethyl lead suflicient'to substantially correct the variation in separate cylinder knocking tendency.

6. Liquid fuel for internal combustion engines of the Otto cycle multicylinder type comprising a mixture of hydrocarbons of such varying vola.

tility and forming such varying air-fuel ratios as to cause material variation inthe knocking tendency of the several cylinders in operation andV containing a small amount of a mixture comprising amounts of tetraethyl lead and of tetra` methyl lead sufllcient to substantially correct the variation inseparate cylinder knocking tendency.

7. A fuel forf high-compression multicylinder internal combustion engines comprising a mixture vof hydrocarbons of such varying volatility as to cause material variation lin the knocking tendency in different cylinders and a relatively small amount of at least one of the following lead alkyls; trlethyl `methyl lead, diethyl dimethyl lead, and ethyl trimethyl lead.

8. The method of operating a multicylinder internal combustion engine during acceleration from low -speeds including supplying to said en# gine a mixture ofair and fuel, the conditions being such that a material portion of the fuel is in liquid form and is -unequally distributed -to they cylinders, and supplying with the fuel mixture a relatively small amount of a mixture of tetraethyl lead and amore volatile lead alkyl than tetraethyl lead.

p oline boiling range and supplying with the fuel mixture relatively small amounts of tetraethyl lead and tetramethyl lead.

10. 'I'he method of operating a multicylinder f internal combustion engine during acceleration from low speeds including supplying to said engine a mixture of air and fuel, the conditions being such that a material portion of the fuel is in liquid form in the intake passages of the engine and is unequally distributed to the cylinders, and supplying with the fuel mixture a relatively small amount of at least one of the following lead alkyls: triethyl methyl lead, diethyl dimethyl lead and ethyl trimethyl lead.'

JOHN' CAMPBELL. 

